Such an incandescent lamp is disclosed, for example, in the European laid-open specification EP 0 986 093 A1. This specification describes an incandescent lamp whose lamp vessel has an interference filter coating with a locally differing layer thickness. The layer thickness of the interference filter varies in such a way that all regions of the lamp vessel which is coated with the interference filter emit light of the same color composition in the switched-on state of the incandescent lamp. The incandescent lamp is designed as an automobile signal lamp emitting orange or red light.
It is the object of the invention to provide an incandescent lamp of the generic type having an improved interference filter for producing red light. An incandescent lamp may be made having a transparent, essentially rotationally symmetrical lamp vessel (20), an incandescent filament surrounded by the lamp vessel (20), and an interference filter (30) which is arranged on the lamp vessel (20) and designed as an edge filter. The interference filter (30) has layers of low optical refraction and high optical refraction for setting the edge of the interference filter (30) in the red spectral region. The layer thicknesses of the layers of low optical refraction and high optical refraction differ locally as a function of the angle of incidence of the light emitted by the incandescent filament and impinging on the interference filter, and the interference filter (30) has absorber layers for absorbing blue and violet light. The interference filter further has at least two of these absorber layers with, in each case, an intermediate layer of low optical refraction arranged therebetween, and additional layers of low optical refraction and high optical refraction for further suppressing light from the violet and blue spectral regions.